1. Field of the Invention
This invention relates to ink jet printing, and more particularly to a gutter for collecting non-printed ink droplets from an ink droplet generator of a pagewidth, continuous stream type ink jet printer.
2. Description of the Prior Art
Ink jet devices of the continuous stream type generally employ a printhead having a droplet generator with multiple nozzles from which continuous streams of ink droplets are emitted and directed to a recording medium or a collecting gutter. The ink is stimulated prior to or during its exiting from the nozzles so that the stream breaks up into a series of uniform droplets at a fixed distance from the nozzles. As the droplets are formed, they are selectively charged by the application of a charging voltage by electrodes positioned adjacent the streams at the location where they break up into droplets. The droplets which are charged are deflected by an electric field either into a gutter for ink collection and reuse, or to a specific location on the recording medium, such as paper, which may be continuously transported at a relatively high speed across the paths of the droplets.
Printing information is transferred to the droplets through charging by the electrodes. The charging control voltages are applied to the charging electrodes at the same frequency as that which the droplets are generated. This permits each droplet to be individually charged so that it may be positioned at a distinct location different from all other droplets or sent to the gutter. Printing information cannot be transferred to the droplets properly unless each charging electrode is activated in phase with the droplet formation at the associated ink stream. As the droplets proceed in flight towards the recording medium, they are passed through an electric field which deflects each individually charged droplet in accordance with its charge magnitude to specific pixel locations on the recording medium. Thus, to calibrate the ink jet printer so that the ink droplets impact the desired locations on the recording medium, the trajectories of the ink droplets must be determined and adjusted in a manner, for example, taught by U.S. Pat. No. 4,255,754 to Crean et al. This patent discloses the use of paired photodetectors to sense ink droplets one each for two output fibers that are used to generate an electrical zero crossing signal. The zero crossing signal is used to indicate alignment or misalignment of a droplet relative to the bisector of a distance between the two output fibers. The sensor of this patent employs one input optical fiber and at least two output optical fibers. The free ends of the fibers are spaced a small distance from each other; the free end of the input fiber is on one side of the flight path of the droplets, and the free ends of the output fibers are on the opposite side. The remote end of the input fiber is coupled to a light source such as an infra-red light emitting diode. The remote ends of each output fiber are coupled to separate photodetectors such as, for example, a photodiode responsive to infra-red radiation. The ink is substantially a dye dissolved in water and is transparent to infra-red light, thus reducing the problems of contamination usually associated with ink droplet sensors. The photodiodes are coupled to differential amplifiers so that the output of the amplifiers are measurements of the location of droplets relative to the bisector of the distance between the output fiber ends confronting their associated input fibers and the droplets passing therebetween. Amplifier outputs are used in servo loops to position subsequently generated droplets to the bisector location. By using one of these zero crossing signal detectors at a location between adjacent endmost droplets thrown from separate adjacent nozzles, the stitch point between these droplets can be controlled so that the segments of each line of droplets to be printed by each nozzle may be adjusted to prevent gaps or overprinting on the recording medium.
U.S. Pat. No. 4,309,711 to Teumer discloses a continuous stream-type ink jet device having an ink droplet guttering system incorporated into every other deflection electrode. The droplets from each nozzle pass through an electrostatic field produced by a pair of deflection electrodes. One deflection electrode in each pair is grounded and is basically hollow with an opening in its trail edge or downstream edge. This trail edge confronts the recording medium so that ink droplets not to be printed are deflected by the electrostatic field into impact with the grounded deflection plate near its trail edge. The momentum of the ink droplet after impact carries the droplet around to the opening in the deflection plate where a light suction draws the ink into the hollow deflection electrode where it may be collected and returned to the ink supply for recirculation.
U.S. Pat. No. 4,347,521 to Teumer discloses a continuous stream type ink jet device having W-shaped or tilted pairs of deflection plates, one of which is grounded, and a separate guttering system that confronts the trail edge or downstream edge of the grounded deflection plates. The trail edge of the grounded deflection plate is tapered to provide clearance for the droplets to be guttered and to prevent impact thereon by the droplets.
U.S. Pat. No. 4,525,721 to Crean discloses a continuous stream type ink jet device which prints according to an interlace strategy. Each ink stream has a pair of deflection plates, one of which is grounded. Each grounded deflection plate contains an integral gutter.
Xerox Disclosure Journal, Vol. 9, No. 4, dated July/August 1984, to Lonis, discloses a continuous stream type ink jet device having a movable gutter which is repositionable between a location to interrupt the ink streams immediately downstream from the nozzles and prior to the charging electrodes and a location out of the paths of the ink streams.